For example, percutaneous bone augmentation includes the techniques of vertebroplasty and kyphoplasty which have been used in the following indications: painful hemangiomas, osteoporotic compression fractures, traumatic compression fractures and painful vertebral metastasis. An example is the percutaneous delivery of polymethylmethacrylate (PMMA) bone cements to repair fractured vertebral bodies. This treatment is effective in relieving pain and restoring height to the vertebrae. The targeted vertebrae are identified using fluoroscopy and a trocar needle is introduced into the vertebral body. The PMMA can be delivered to one (unilateral) or both (bilateral) sides of the vertebral body and the delivery is monitored using fluoroscopy to ensure that the cement remains a bolus, without leakage or migration.
Complications of the technique include leakage of PMMA. This can be paravertebral leakage, venous infiltration, epidural leakage and intradiscal leakage (Truckai C., Shadduck J. H., US 2006089715, 2006). Leakage can result in very serious complications including compression of adjacent structures (requiring further surgery) and/or embolism. Recent research has also demonstrated that a mismatching of forces between the PMMA and natural bone leads to an increase in secondary fractures in the vertebrae adjacent to the PMMA treatment (Trout A. T., Kallmes D. F., Kaufmann T. J., Journal of Neuroradiology, 2006, 27:217-223).
A further complication of the technique is the high exothermicity of PMMA that can potentially cause heat necrosis extending to the dural sac, cord and nerve roots. This exothermicity also limits the ability of PMMA to incorporate any pharmacological or chemotherapeutic agents. PMMA is also a non-resorbable material and is capable of leaching unreacted, unpolymerised and low molecular weight chemicals. For the technique a fluoroscopic contrast agent (usually barium sulphate) is incorporated in the PMMA cements to facilitate the fluoroscopic delivery. The long term effects of barium sulphate on the bone and the cement properties are not fully known.
The viscosity of PMMA is also a critical parameter. It must be low enough to permit injection and high enough to prevent it from being squeezed into the vasculature. The viscosity rises with time providing the clinician with a window of approximately 10 minutes to perform the technique and retrieve the needle.
Thus, a strong need exists for injectable bone augmentation compositions which overcome the above-mentioned disadvantages.
Therefore, it is an object of the present invention to provide new injectable compositions for bone augmentation, such as in vertebroplasty and kyphoplasty.